Engines produce a number of exhaust gases, some of which are considered environmentally undesirable. One of these by-products is NO.sub.x compounds. NO.sub.x compounds are generated during the combustion of hydrocarbon fuels, especially at increased combustion temperatures.
Exhausting NO.sub.x, whether into air or water, has detrimental effects on the environment. NO.sub.x exhausted into the air may either photoreact and create air pollution or chemically react and contribute to acid rain. NO.sub.x which is discharged into water, such as from outboard motors, is readily converted in reduction-type chemical reactions into acid. It has been found that even small changes in pH caused by the introduction of acid into a body of water may have an undesirable effect on plants and wildlife. As a result of these and other concerns regarding the effects of the engine exhaust, many principalities now regulate NO.sub.x output.
Controlling the exhaust gas content of engines, both those in automobiles and outboard motors, meets with some difficulties. The engine of an outboard motor is positioned within a very small housing or cowling. Likewise, the engines of newer automobiles must often be positioned in very small engine compartments. In both situations, little space remains apart from the base engine components for emission control equipment. In addition, high engine and emission control component temperatures are sometimes incompatible with certain engine components. In addition, the emission control components generally increase the complexity and cost of manufacture and assembly of the engine.
An apparatus and method for use in controlling the content of the exhaust gas produced by an internal combustion engine is desirable.